This invention relates to an eccentric orbiting type speed changing device for performing deceleration or acceleration by eccentrically rotating pinions or transmission disks.
As a conventional eccentric orbiting type planetary reduction gear device, for example, known is such a device comprising a casing having an internal gear at an inside periphery, two sheets of pinions held in the casing separately in an axial direction and defined on an outside periphery with external gears to be in mesh with the internal gear, a carrier having a pillar-like portion passing through the pinions in the axial direction, and an eccentric crank shaft causing these two sheets of pinions to eccentrically rotate under a condition of deviating phases thereof by 180 degree.
However, the conventional eccentric orbiting type planetary reduction gear device has a big problem generating large vibrations and noises.
An inventor of this patent application made earnest studies on mechanisms generating vibrations and noises in the eccentric orbiting type planetary reduction gear device, and came to the following findings. Namely, when the eccentric orbiting type planetary reduction gear device 11 reduces the speed as shown in FIGS. 7, 8 and 9, the gearing engagement in an X direction (tangential direction) as well as the gearing engagement in a Y direction (radius direction) act on respectively from the external gears of the pinions to the internal gear of the casing 12 by the rotation of the pinions 13, 14. Further, the pinions 13, 14 are respectively acted by the centrifugal force in the Y direction by the revolution thereof. At this time, the engaging forces Fx and Fy in the X and Y directions in the pinion 13 as well as the engaging forces -Fx and -Fy in the X and Y directions in the pinion 14 are equal in values, but the working directions are reverse, and the centrifugal forces P and-P in theY direction in the pinions 13, 14 are equal values but the working directions are reverse. Consequently, the resultant force of the engaging forces in the X and Y directions and the resultant forth of the centrifugal force are made zero and balanced with respect to the force. Herein, it is presumed that the engaging force is a single force acting on center flat faces a, b in the gear width of the pinions 13, 14 in a maximum engaging parts of the pinions 13, 14 and the casing 12, and on the other hand it is presumed that the centrifugal force is a single force acting on the center of gravity of the pinions 13, 14. However, when observing the engaging forces Fy and -Fy in the Y axial direction and the centrifugal forces P and -P in the pinions 13, 14 on the flat faces including Y and Z axes together as shown in FIG. 10, both engaging forces Fy, -Fy and the centrifugal forces P, -P are separatedby a distance L, and consequently couple of forces of Mf=Fy.times.L (moment of rotation) and couple of forces of Mp=P.times.L (moment of rotation) are created by both engaging forces Fy, -Fy and the centrifugal forces P, -P,, and accordingly the resultant force of the engaging force and the resultant forth of the centrifugal force are imbalanced with respect to the moment of rotation in the prior art. Since such moment of rotations (couple of forces) are imparted to a crank pin 15 and are gradually deviated toward a circumferential direction following eccentric rotations of the pinions 13, 14, the eccentric orbiting type planetary reduction gear device 11 is periodically vibrated to cause large vibrations and noises.